1. Field of the Invention
The invention relates to an automatic screwing device with automatic screw supply, in particular a hand screwdriver of this kind, comprising a screw driving tool and a collet for holding a secured, protruding screw, in which the screw driving tool is coupled to an actuating device for the generation of a rotary movement and a feed of the screw driving tool, which takes place relative to the collet, wherein the actuating device has a rotationally drivable, first threaded element, which is connected to the screw driving tool and has a first thread, and also at least one second threaded element, which stands in working engagement with the first threaded element via the first thread.
2. Description of the Prior Art
In such known automatic screwing devices, the actuating device is, for example, driven by means of an air motor to produce the rotary movement and by a pneumatic piston-in-cylinder unit to produce the feed.
Disadvantageous in the use of air motors and pneumatic piston-in-cylinder units is the fact that two different actuating devices are required to produce the rotary movement and the feed, namely an air motor and a pneumatic piston-in-cylinder unit, which is naturally associated with additional manufacturing costs.
Furthermore, it is of disadvantage that the operation of the two actuating units is, on the one hand, associated with a relatively loud noise, and, on the other hand, that the air which acts on the motor and the piston must be oiled, which often leads to undesired contamination as a result of the not completely avoidable oil spray.
An automatic screwing device is known from EP-A-0 284 755, in which the rotary drive and the feed are driven from a single drive shaft. A first threaded element in the form of a splined shaft is rotationally fixed, but axially displaceable within the drive shaft. The splined shaft is connected via a thread to a second threaded element in the form of a spindle such that, on rotation of the splined shaft via the drive shaft, the splined shaft executes an axial movement together with the screw driving tool secured thereon. Disadvantageous with this automatic screwing device is the fact that, with a constant rotation of the drive shaft, the return travel of the screw driving tool for the purpose of a renewed automatic screw supply involves a comparatively long dead time.
An object of the invention is to further develop an automatic screwing device of the initially named kind, so that it can be manufactured less expensively, in particular with both the rotary movement and also the feed being produceable by a unitary actuating device. At the same time, a high working speed of the automatic screwing device should be made possible.
In accordance with the invention this object is satisfied in that the second threaded element is connected to the collet, and in that two different feed speeds can be produced for a constant speed of rotation of the first threaded element by the provision of two different thread pitches at the first thread and at a second thread, which is provided on the first threaded element or on the second threaded element.
Thus, in accordance with the invention, in distinction to the prior art, the feed movement is ultimately also derived from a rotary movement, and both the rotary movement and also the feed movement can be produced by means of two cooperating threaded elements. In this arrangement, different speeds of advance can be produced through the provision of two different thread pitches. These different speeds of advance are of substantial importance for an operation of the automatic screwing device taking place with a higher cycle rate, since, in automatic screwing devices with an automatic screw supply, measures must be taken to ensure that the screw driving tool can be retracted very rapidly out of the region of the collet after a screwing procedure has been completed in order to avoid a newly supplied screw colliding with the screw driving tool during the supply procedure. After the new screw has been supplied, measures must again be taken quickly to ensure that the screw driving tool is moved into the region of the collet, since the newly supplied screw must be held there by the screw driving tool in the normal manner by elements of the collet which are resiliently biased.
When, thereforexe2x80x94as in the inventionxe2x80x94a rapid movement of the screw driving tool is made possible away from the collet and subsequently back to the collet again, it can be ensured that a new screw can be supplied in the shortest possible time after a screwing procedure has been completed and can be held as a secured, protruding screw between the collet and the screw driving tool. A screw held in this manner is then ready for a new screw driving process.
If now, in accordance with the invention, two different speeds of advance can be provided despite constant speed of rotation of the first threaded element, then, on the one hand, a rapid relative movement between the screw driving tool and the collet is made possible and, on the other hand, it is ensured that the pressing of the screw out of the collet, which is required during the screwing process, takes place with a lower speed of advance and thus adequately slowly, so that a problem-free screwing procedure is ensured.
In accordance with the invention both the rotary movement of the screw driving tool required for the screw driving process and also the feed required for the operation of the automatic screwing device are achieved by a rotation of the first driveable threaded element. The rotating drive of the threaded element can in this respect be effected, for example, by means of an electric motor fed from a power supply or from an accumulator. Thus, in accordance with the invention, it is no longer necessary to use a pneumatic piston-in-cylinder unit or an air motor. The disadvantages which are known from the prior art are thus removed by the invention.
At the same time it is, however, ensured that no penalties have to be tolerated with respect to the operating speed or cycle rate of the automatic screwing device, since, as a result of the two different speeds of advance, an adequately rapid manner of operation of the automatic screwing device can be ensured.
It is preferred when the first threaded element is formed as a threaded spindle (first thread) and the second threaded element is formed as a nut. The nut can, in this case, have an internal thread (first thread) which cooperates with the threaded spindle and an external thread (second thread) which cooperates with a sleeve element, with the sleeve element then having a corresponding internal thread (second thread) and preferably being connected to the collet.
Through a rotation of the threaded spindle, a situation can then be achieved in which the nut, on the one hand, is moved along the axis of the threaded spindle. On the other hand, through a rotation of the nut which takes place jointly with the threaded spindle, for example after the nut running along the spindle has reached its abutment position, a situation can be achieved in which the sleeve element moves along the axis of the nut, which coincides with the axis of the threaded spindle.
If now the thread active between the sleeve element and the nut has a different pitch than the thread active between the threaded spindle and the nut, then different relative speeds can be achieved between the threaded spindle and the sleeve element by a rotary movement of the threaded spindle with a constant speed of rotation. Since the threaded spindle is connected to the screw driving tool and the sleeve element is connected to the collet, different relative speeds are accordingly also achieved between the screw driving tool and the collet.
Since the threaded spindle is, as a rule, fixedly coupled to an electric motor which is arranged in a fixed position in the housing of the automatic screwing device, it is of advantage, in accordance with the invention, when the screw driving tool executes no feed movement relative to the housing of the automatic screwing device, but rather if the collet is instead retracted relative to the screw driving tool. In the end result, this retraction of the collet is the same as a feed movement of the screw driving tool relative to the collet.
Since the path of advance required for the screwing procedure is smaller than the path of advance required for the retraction of the screw driving tool from the region of the collet, it is sensible, in the context of the invention, to make the pitch of the inner thread of the nut or the pitch of the thread of the threaded spindle larger than the pitch of the external thread of the nut or of the internal thread of the sleeve element. The sleeve element and the nut have a smaller axial extent than the threaded spindle, so that with the aforementioned pitch relationships a rapid feed movement can be produced over the relatively large axial extent of the threaded spindle and a comparatively slow feed movement can be produced over the comparatively small axial extent of the nut or sleeve element.
In order to ensure that the nut always first moves along the threaded spindle and the sleeve element is only then moved along the nut, starting from a position in which the nut and the sleeve element are both located in a forward abutment position, or are both located in a rear abutment position, the outer thread of the nut can be more difficult to turn in conjunction with the sleeve element than the inner thread of the nut in conjunction with the threaded spindle. Thus, the nut will always first move into its abutment position relative to the threaded spindle before a relative movement sets in between the nut and the sleeve element.
The above feature can be most simply realized if the threaded spindle is executed as an easily turning ball spindle, and the outer thread of the nut is executed as a fine thread.
In order to control the speed of rotation of the screw driving tool during the screw driving process, the rotary speed of the first threaded element, i.e. of the threaded spindle, can be regulatable, at least during the action of the thread having the smaller pitch, i.e. for example the outer thread of the mut.
The automatic screwing device of the invention is preferably provided with a clutch which serves for the decoupling of the rotary movement of the first threaded element from the thereby produced feed movement. Through such a clutch a situation is achieved in which an axially directed relative movement between the collet and the screw driving tool does not always necessarily take place on a rotation of the first threaded element. The said clutch is in particular so designed that it can bring about a decoupling of the rotary movement and the feed when a screw has been fully pressed out of the collet as a result of a feed movement which previously took place.
No further feed is namely any longer necessary as soon as the screw has been fully released by the collet. It should, however, still be possible to complete the screw driving procedure. As a result, it is advantageous if, in this case, when the screw is no longer held in the collet, a continuation of the screwing process or of the rotary movement of the screw driving tool can take place without the simultaneous production of a relative axial movement between the screw driving tool and the collet. Precisely this is achieved by the said clutch.
The clutch is preferably provided in the already named sleeve element and is in particular realized by means of a first cone and a second cone, the cooperation of which can be cancelled at the instant in which a screw has been fully released by the collet.
The first cone can in this respect be connected to an element of the sleeve, which has the inner thread of the sleeve. In just the same way it is possible to provide the first cone directly with the internal thread of the sleeve.
The second cone, which can be provided radially outside of the first cone, is advantageously connected directly or indirectly to the collet. In this way a situation is achieved in which an axially directed relative movement between the screw driving tool and the collet always takes place when the first cone is in engagement with the second cone, i.e. if the clutch has not been released, as soon as the threaded spindle is set rotating. Only if the first cone has been released from the second cone does a rotation of the threaded spindle bring about no axially directed relative movement between the collet and the screw driving tool. In the last-named case, the rotary movement of the threaded spindle produces only a rotary movement of the screw driving tool, which is, for example, necessary in order to complete a screwing process after the screw has been released from the collet.
It is advantageous if, in the context of the invention, the nut and the sleeve are exchangeable, since in this case different sets of nuts and sleeves can be made available, which can be provided with different thread pitches. These thread pitches between the nut and the sleeve ultimately determine the speed of the axially directed relative movement between the screw driving tool and the collet during the screwing in of a screw. Since, as a result of making available different sets of nuts and sleeves, different speeds can be selected with respect to the said relative movement, it is possible, through the intentional use of a specific nut/sleeve unit, to adapt the speed of the said relative movement to the pitch of the thread of the respectively used screw.
The invention can be used particularly advantageously when a screw supply or a screw magazine is provided for the automatic feeding of screws into the collet, with the screw supply in particular being designed as a pivotable supply channel.
The pivotable supply channel can, with the automatic screwing device formed in this way, always be pivoted into the region of the collet for the purpose of supplying a screw when the screw driving tool has been retracted by the first threaded element, or by the threaded spindle, out of the region of the collet. By a movement of the screw driving tool, which takes place into the region of the collet after the supply of the screw, the supply passage, which is in particular resiliently biased, is pressed by the screw driving tool out of the region of the collet and the screw driving tool comes into engagement with the screw head, whereby the screw is ultimately fixed in the collet.
It is, furthermore, advantageous if a screw magazine is coupled to an automatic screwing device in accordance with the invention in such a way that the supply of a screw from the screw magazine can be triggered through a retraction and subsequent advance of the screw driving tool or through an advance and subsequent retraction of the collet. In particular, it is possible in this wayxe2x80x94in similar manner to a magazine principle known in the field of weaponryxe2x80x94to couple in the screw magazine in such a way that a screw supply channel can be freed for the purpose of supplying a screw from the screw magazine by the retraction and subsequent advance of the screw driving tool, or by the advance and subsequent retraction of the collet.
In a preferred method for the operation of an above-described automatic screwing device the screw driving tool and the collet are moved relative to one another between a basic position, a screwing-in position, a first retraction position and a second retraction position.
In the basic position a secured, protruding screw is held in the collet. In the screwing-in position, a tightening of the screw takes place. In the first retraction position, or during the movement from the first retraction position into the second retraction position, a supply of a new screw to the collet takes place.
After the supply of a new screw a movement of the automatic screwing device then takes place, preferably automatically, into its basic position, from which a new screwing process can be initiated with a secured, protruding screw.
With a design of an automatic screwing device with a threaded spindle, nut and sleeve, it is preferable if the spindle and the nut are arranged relative to one another in the basic position in an abutment position, in which the screw driving tool has been moved as far as possible in the direction of the collet. The sleeve is then located relative to the nut in the abutment position in which the distance between the screw driving tool and the collet is still as large as possible. Starting from the basic position, a movement of the screw driving tool can then consequently only take place in the direction of the collet in that the sleeve and the nut are moved relative to one another in a corresponding direction.
It is particularly preferred if, in the basic position, a small movement between the sleeve and the nut has already taken place in the direction in which the screw driving tool is moved in the direction of the collet, since in this way screws with differently sized screw heads can be held in a defined manner in a resiliently pre-stressed collet. The described, relative position between the sleeve and the nut in the basic position namely brings about a situation in which, with differently sized screw heads, the collet is opened up to a greater or lesser degree in accordance with its resilient pre-stress, so that screw heads of different sizes can in any event be firmly held between the collet and the screw driving tool by the resilient pre-stress of the collet.